This invention relates to a torque-adjusting device for use in a roller blind of the type having a built-in spring-motor to roll up a screen.
A roller blind has a roller assembly supported by a pair of mounting brackets and provided with a hollow roller on which a screen is wound. A spring-motor is contained in the hollow roller and has one end thereof secured to a stator and the other end fixed to a rotator which is integrally secured to the hollow roller. In general, the stator is preliminarily wound before the roller assembly is mounted in the brackets to give an initial torque to the spring-motor for the purpose of surely rolling up the screen drawn down. The initial torque is desirably adjusted to such a value in which the screen is lightly pulled down by one's hand and smoothly rolled up by the spring-motor. The optimum value can not be decided without several trials of adjustment, because it depends upon many factors, for example, the machanical property of the screen as well as the spring-motor. The trial is made to give the optimum torque to the spring-motor as follows: The stator is gradually rotated in one direction to increase the torque in the spring-motor if the screen is weakly taken up but inversely rotated little by little if it is somewhat heavy to be pulled down by one's hand.
The known device comprises the stator directly mounted in the mounting bracket. This leads to a disadvantage that the spring-motor can not have the initial torque thereof adjusted unless the roller assembly is removed from the mounting brackets. It is very troublesome to put off the roller assembly from the permanent position and reset the same in the original position several times for torque-adjustment until the spring-motor has the optimum initial torque.
It is the primary object of the invention to provide a torque-adjusting device for use in a roller blind of the type having a built-in spring-motor, in which the initial torque in the spring-motor is easily adjusted while the roller assembly is set up in the permanent position.